# Interest and rate of cost

8) Warren calls home from Iraq at a rate (in dollars) of $2.25 for the first minute plus $.20 for each additional minute. If his total bill for the call is $11.65, then for how many minutes did he talk altogether? (Don't forget the first minute).

9) Lindsey is driving on the Beltway on her way to the UMUC campus. Her car is rear-ended. Fortunately no one is injured, but the bill for the car repair is $1650. The cost for parts was $1380. If the cost of labor was $45/hour, how many hours did the repair work take?

10) Mike won the lottery last year and had a total of $300,000 (after taxes) that he wanted to invest immediately. His invested a portion of the total in a 1-year CD that paid 5% annual interest and the rest in a mutual fund that paid 8% annual interest. If he earned a total of $16,500 in interest by the end of the year, how much did he invest at each rate of interest?

If Mike had reversed his investments in problem #10, how much interest would he have earned in that year?

6) The formula for simple interest is I=PRT , where I is the interest earned, P is the principal (or initial amount deposited), R is the annual simple interest rate in decimal form, and T is the time in years. If Inez invests $1000 at an annual rate of 6% simple interest, how much interest will she earn in 5 years?

7) If the area of a circle is given by , and an extra-large pizza has an 8-inch radius, approximately what is the area of an extra-large pizza? Round your answer to the nearest whole number.

#### Solution Preview

8. Assume he talked x minutes totally.

For the (x -1) minutes after the first minutes, the charge is 0.2(x - 1).

So the total bill is

2.25 + 0.2(x -1) = 11.65

0.2(x -1) = 9.4

x - 1 = 9.4/0.2

x - 1 = 47

x = 47 + 1

x = 48

He talked 48 minutes.

9. The total cost = Cost of parts + Labor.

So the labor itself = total cost - cost of parts = 1650 - ...

#### Solution Summary

This is a set of questions regarding interest and rates of cost.